In the installation of service pipes for the supply of fluids it is known to place over a length of pipe or over the ends of two lengths of pipe of thermoplastic material a respective tee-piece fitting or a tubular fitting of thermoplastic material having an integral electrical heating wire adjacent its inner surface and to energise the heating wire so that the material of pipe(s) and fitting become soft and form a welded fusion bond with each other. With such thermoplastic fittings it is important that the energizing current is applied for the optimum time necessary to effect perfect fusion since applying the current for too short a time may result in a leaking joint while applying the current for too long a time may overheat and damage the fitting and also result in an unsatisfactory joint. An example of one such fitting is described in our copending UK Patent Application No. 2090558A.
In practice the fittings for use in quite different conditions and requiring quite different periods of energisation may be similar in appearance and therefore it is important that there is a reliable method of identifying them so that the correct energisation period can be selected and so that the energisation can be carried out automatically.
An object of this invention is to provide a coupling device for use with an electrofusion fitting of thermoplastic material to provide positive identification thereof.